Signal-seeking receiver



May 9, 1950 R. A. Gum.

SIGNAL-SEEKING RECEIVER Filed June '7. 1946 KN S EN@ EN@ Patented May 9, 195() UNITED STATES PATENT FFICE SIGNAL-SEEKING RECEIVER Roy A. Gull, Kenmore, N. Y., assigner to Colonial Radio Corporation, Buffalo, N. Y.

Application June 7, 1946, Serial No. 674,965

(Cl. Z50-40) Claims. l

This invention relates to improvements in signal-seeking receivers, and more particularly to such receivers arranged to provide more accurate tuning to the incoming signal.

For the purposes of this speciiication, a signalseeking receiver is defined as a receiver in which the tuning instrumentality is power driven, for instance by an electric motor, and when set into operation scans its tuning spectrum until an incoming signal of predetermined strength is tuned in.

At this point the incoming signal voltage operates a rel-ay, through the medium of a control tube, which de-energizes the tuning motor and in addition may de-clutch the tuning m'otor from the tuning instrumentality and apply a brake to the tuning instrumentality so that the receiver remains tuned to the desired signal.

This action is purely automatic and requires no care or attention and no skill on the part of the operator. Also, if the apparatus is properly designed and constructed, it will tune the incoming signal more accurately than can possibly be done manually.

If the operator wishes to change to another station, all that is necessary is momentarily to operate a push button, which starts the tuner motor in operation, releases the brake, clutches the motor to the tuning instrumentality (if clutch and brake are employed), and the tuner will scan until another incoming signal of predetermined strength is received, whereupon the receiver deenergizes the motor and remains tuned to the particular signal until the operator again sets it in operation to look for another station.

In apparatus of the type heretofore proposed, it has been suggested to utilize a portion of the output of the intermediate frequency amplifier, which portion is then passed through a limiter, and the output of the limiter is then passed through a balanced tuned bridge circuit embodying a piezoelectric crystal tuned to the center frequency of the intermediate frequency band. The voltage from this tuned bridge circuit is then used to control a vacuum tube having a relay in its plate circuit, and this relay controls the tuner motor and the clutch and brake mechanism, if employed.

In such receivers it is customary always to tune in the same direction; that is, the motor always runs in the same direction; for instance, in a direction to scan the tuning spectrum from the low frequency end to the high frequency end. Usually some form of quick return motion is provided in the tuner drive so that when the tuner reaches the high frequency end of the spectrum, it snaps back very quickly to the low frequency end. An arrangement of this nature is disclosed in the Nicholson U. S. Patent No. 2,487,772, dated November 8, 1949, entitled Signal-seeking receiver for AM and FM signals and assigned to the same assignee as is this patent.

If this snap-back is sufficiently rapid, it is not necessary to mute the high-frequency signal translating channel of the receiver during the return period of the tuner as might otherwise be necessary to avoid premature termination of the receiver tuning on an undesired signal received during the return period. This is because there .is not sufficient time for any signal which may be tuned in during the return stroke or flyback to build up to a sufficient energy level to operate the signal-seeking control system to stop the scanning. Generally the return or yback takes place in about one-tenth of a second, whereas the scanning rate when the receiver is scanning for a signal is about 200 kc. per second. Y

in broadcast receivers which are usually built to cover a range from about 535 kc. to 1620 kc., the total scanning time for the receiver to tune from the low frequency end to the high frequency end is in the order of 5 seconds. Faster scanning is undesirable because the receiver may pass over a desired station while the operator has his finger on the starter button, and slower scanning is undesirable because of the excessive time required to travel from Vthe low frequency to the high frequency end of the spectrum.

One diniculty which may be encountered in receivers of this type is mistuning resulting from failure of the apparatus to stop instantaneously when the incoming signal voltage reaches a level high enough to operate the relay to stop the motor. This results from inertia in the various movable parts, such as the relay, armature, the motor, and the clutch and brake mechanism, if clutch and brake are employed.

In general, a time interval of the order of about 2 milliseconds elapses between the time when the incoming signal voltage reaches a level suiiicient to trip the relay and the time when the tuning instrumentality actually comes to rest. If the scanning occurs at the rate of 200 kc. per second, this results in the receiver being detuned from' the desired signal by approximately 400 cycles.

In accordance with my invention, this difculty is eliminated by tuning the control circuit, not to the exact center of the intermediate frequency band, but to a frequency lower than this by an amount equal to the number of cycles scanned per second multiplied by the time interval in seconds which the particular receiver requires between the time the signal voltage reaches a value sufcient to trip the relay and the time the tuning instrumentality actually comes to rest.

If the scanning is done from the high frequency to the low frequency end of the spectrum, the offset in frequency will be made higher than, in.'- steadV of lower than, the center of the intermedi- 3 ate frequency band by the same amount. The resultl of this is that the control circuit is set into operation by a time which is just enough so that, when the tuning instrumentality has actually come to rest, it is tuned very closely to the desired signal frequency.

From the foregoing, it will be understood that it is an object of this invention to/provide increased accuracy of tuning in-a signal-seeking receiver. Y

It is a further object of this invention to provide for increased accuracy of tuning Vin such a, receiver Without the use of compensating circuits such as heretofore proposed. Itis a further objectof this invention to pro- Ivideincreas'ed accuracy of tuning in such a receiver without changing 4Vthe constants of the Aos illjatorcir'cuitas has heretofore been proposed. K l.Still .other objects and advantages ofrny inventio'n 'ivill be 'apparent from the specification. '-Tlie features 'ci novelty which I believe to be aracte'ri'stic of 'my 'inventionfare v'set forth with if) la'jrity inthe 'appended claims. My inven- 'tion itself, however, both as Vto its fundamental brifncinl'es and as toits particular embodiments, Will'bes't be understood byreference to the specilcation and accompanying dr'atving, "in which ":Ihefs'ingl'e figure is a circuit diagram of an im- Referring-'nowriiore particularly to the drawingA l .repifesents'anantenna of any suitable type, ieiiingr'adiofrequency amplifier and converter il tuned by any suitable tuning instrumentality, herein .indicated -as 'gangjcondenser lia. cutout 'of `the lconverter is then supplied to internediate "frequency amplier l2 and thence to detector `rand audio Va'mpliiier I3 and loud speakel* T4.

lm accordance with the embodiment of the inven ion herein shown and described, and which Wil'l'be understood to be merely by way of example, since 'other arrangements may be employed, a 'loof i`o`n ofi 'the output of intermediate frequency amp fier- 12 is imnres'sed upon limiter I5. This ,mjayjand usually will, be a limiting amplier tube 'having ycai-,luide lic, control `electrode 15g, screen A11.530, suppressor i531, Vand anode 15a.

a vczfltnoue rse will usually be connected to ground ltnrougnseir-bios'ing resistor let shouted by byl nasscnde'nser me, and control electrode I5g is V connected to gro'und'through resistor 16a. Resistor "Ito may bey/onecle if desired, for the lpurse fo'f controlling tthe level oi the incoming athod'as usual.

he A"ecorl'dary VWinding '42 0i transformer '40 firiay haveone terminal vconr'iected to `one 'termi- 'iraloff 'niezoelectriccrystal 2Q and the 4'other terinal connected through condenser kt6 "to 'the y termino-1er crystal 2e. Winding 42 `maybe shnnted by c'ondensersM and l5 in series, having their lcommon 'terminal grounded. Y

"'Theioutput'lof the tuned bridge circuit may be "supp reo to rectifier 22, which iin this 'instance yjtjea triodefconnctedas a diode, having-cathezfa grid 12g, and anode-"22a, the latter two The i' 'i slg'r'ial atftthich the receiver will stop scanning. Y

'condje'r'iser'l. Suppressor lsr is connected toA d "signal-'seekin"greceiver in accordance with being connected together and to the common terminal of crystal 2D and condenser 46.

Cathode 22c may be connected to ground through resistor 123 shunted fby condenser 24, and may be also connected to"`B-{ through resistor 2.5. yGfrid and anode 22g and 22a may be connected together, to ground through resistor 21, and thv'nghlresistor 26 to control electrode 28g of tube 28, having cathode 28e, control electrode 'zqa'nd Yanode '2`8a.

Anode y28a is connected through energizing .ivindinglfzwiofrlay 29 and through resistance 31D to B+. The stationary contact 29j of relay Zlfim'ay be connected toground and the movable contact 29a of the relay is connected to statiola'jry cO'ntactSM-f -r'elay `:'34, the 'movable con- 'tact 334o', "of 'Wifi-ich Y'may be vConil'el'."tet through starter Vvsvvit'ch 35 vto ground 1 and also vto 'one -s'ide of 4the tuning motor 3`2*ha-ving 1an 'armature `32a fand/field Winding 32%. The energizing winding "lw ci ytheir-clay 3d is connected across fthe finotor 'a-rn ture 32a.

'The'other side 'of the Amotor v"ar-mature and 'iield 'ivi'n'di'n'gfmay be V connected through a suitable :sourceofcurrentil to ground.

vI n accordance with my invention, the tuned bridge Ecircuit is `tuned foif `the center frequency 'ci the intermediate ifrequency band by anl amount wr ich is lequal fto the product o' 'the scanning irate in q"cy'cles'fper second *multiplied by Ithe "time in seconds required'for-the tuning instrumentality 'to Vcorrie to a v"standstill after the signal Tvoltage reaches a value`suiiicientto operate relay'29.

'1i lthe scanning 'is from 'the low 'irequencyend 'tof'the highfirequency end, ithedetun'ing Willbe `in"'the-direction-oi` the low"frequency, and if'ithe 'scan1'ring "is fro'r'n the 1high frequency -end toward theovv -frequency end, 'the 'ie'tu'ning will be in the direction of the high frequency.

V'Fo''ne'X`a 'rr1:le,ii'ithe receiver isdesignedto scan frornlowtohigh frequency at a lfateci r20H-kc. 'per 'secondandthe `'stopping time of the tuning t'ijstrumentalityis-"5 'milliseconds after the signal 'voltage 'l reaches *a f-value sufficient 'to trip relay 29 'and ifthe-iritermediate linermency is 455 kc., then tire Atuned -'lol'igflifc"circuit will be detuned T1100() :cycles it''w'ard the lovvffrequency'end f the 'spectrom, anujtheoriuge ircuitlanu erysteii wiube tuned tol`454Q0'k'c. :it everythnge'lseis thei'same, and the receiver 75Vis designed Avto scan 4Vfrom the j liigh Vfrequency end tol theflow frequency end of Cthe spectrum th etunedbrid'ge'circuit Woulidthen die: llY'edO 4551i) kc.

VVVIn some receivers, vinstead oi a tuned Ebridge uit, "aso-calledlfrequency"idiscriminato'r jnetisr employed tio-operate the control circuit. 4lilly invention may 'fbe ka'Jplied to -fsu'ch 'receivers rin fthe sar'ne Way 3as herein fdes'cribed, "the fcr's's- {'ver #point fof `the A"discri nina-tor being Vdetunei m lil the center 'of `Ithei'ntrrnedia'te "frequency t rid bytlie-'salio amolmthefenpf embed; the-Isc'arining rate in 'per -second -rnulti by the time in seconds required for th'etun'ifng instrumentality to Astop m'ovin'g after th'e iincom- 'ing signal voltage be'co'mes -suic'ie'nt 'to ftrip th'e frel'ay.

Ivi

be open. The motor circuit is, therefore open, and the receiver will remain tuned to the incoming signal.

If the operator wishes to select another station, he will momentarily close switch 35. This closes the motor circuit independently of relays 29 and Slt and causes the tuning instrumentality to start scanning. As soon as motor 32 is energized, relay Se is likewise energized and closes its contacts 34a and 3&1', no output of the intermediate frequency amplifier is impressed on tube l5, no currents are rectied by tube 22, the bias on tube 23 due to incoming signals disappears, and that tube begins to draw normal plate current which is sufficient to close relay 29.

Since relay 3d is already closed, this completes the motor circuit through relays 29 and 34, the latter being locked in, and the operator may now release switch 35, permitting it to open, without stopping the motor. The receiver will continue to scan until the next signal of predetermined strength is tuned in, at which time tube l5 again impresses intermediate frequency currents through crystal 20 on rectier 22, which in turn biases tube 2t to a point where relay 29 opens, thereby de-energizing the motor circuit and bringing the tuning instrumentality l la to a stop.

As already pointed out, because of the tuning of the bridge circuit to a frequency removed from the intermediate frequency by an amount necessary to provide compensation for the stopping time of the tuner, the process of stopping begins just sufiiciently ahead of the correct tuning position so that the inertia of the system causes it to coast to the exact tuning position, giving an accuracy of tuning which is much greater than even a skilled operator can obtain manually, and at the same time requiring no compensation circuits in the converter, as heretofore employed.

In the specications have explained the principles of my invention and the best mode in which I have contemplated applying those principles, so as to distinguish my invention from other inventions; and l have particularly pointed out and distinctly claimed the part, improvement, or combination which I claim as my invention or discovery.

While I have shown and described certain preferred embodiments of my invention, it will be understood that modifications and changes may be made without departing from the spirit and scope thereof, as will be clear to those skilled in the art.

claim.

l. A signal-seeking superheterodyne receiver having` a variable tuning instrumentality, power operated means for varying said tuning instrumentality, manual means for causing said power means to vary said tuning instrumentality, and means for causing tuning in of a signal of predetermined strength to stop variation of said tuning instrumentality, said last mentioned means comprising a frequency selective circuit tuned to the middle frequency of the intermediate frequency band plus or minus the number of cycles by which the tuning of the receiver changes in the interval between the time when an incoming signal voltage reaches a value suflicient to stop the tuning variation and the time when the tuning instrumentality stops varying.

2. A signal-seeking superheterodyne receiver having a variable tuning instrumentality, power operated means for varying said instrumentality,

manual means for causing said power means to vary said tuning instrumentality, and means for causing tuning in of a signal of predetermined strength to stop variation of said tuning instrumentality, said receiver being arranged to scan its spectrum always in the same direction when seeking signals, and said last mentioned means comprising a frequency selective circuit detuned from the middle frequency of the intermediate band by the number of cycles by which the tuning of the receiver changes in the interval between the time when an incoming signal voltage reaches a value suicient to stop the tuning variation and the time when the tuning instrumentality stops varying, said detuning being in the opposite sense from the sense in which said receiver scans its spectrum.

3. A signal-seeking superheterodyne receiver having a variable tuning instrumentality, power operated means for varying said instrumentality, manual means for causing said power to vary said tuning instrumentality, and means for causing tuning in of a signal of predetermined strength to stop variation of said tuning instrumentality, said last mentioned means comprising a frequency selective circuit tuned to a irequency of the order of the middle frequency of the intermediate frequency band but diiering therefrom by an audible frequency.

4. A signal-seeking superheterodyne receiver having a Variable tuning instrumentality, power operated means for varying said instrumentality, manual means for causing said power means to vary said tuning instrumentality, and means for causing tuning in of a signal of predetermined strength to stop variation of said tuning instrumentality, said last mentioned means comprising a frequency selective circuit tuned to a rrequency of the order of the middle frequency of the intermediate frequency band but differing therefrom by a relatively low frequency.

5. A signal-seeking superheterodyne receiver having a variable tuning instrumentality, poweroperated means for varying said tuning instrumentality, and a control system responsive to the reception of a signal of predetermined strength to stop Variation of said tuning instrumentality, said system including a piezoelectric crystal resonant at a frequency diiering from the mean frequency of the intermediate-irequency pass band of said receiver by the number of cycles by which the tuning of the receiver changes in the interval between the time when the received-signal voltage reaches a value suincient to eifect deenergization of said power-operated means and the time when the tuning instrumentality comes to rest.

ROY A. GULL.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,044,645 tapleton et al June 16, 1936 2,056,200 Lowell Oct. 6, 1936 2,218,905 Cooper Oct. 22, 1940 2,369,542 Dietrich Feb. 13, 1945 OTHER REFERENCES Wireless World, Oct. 18, 1935, Article Aerodyne Aeromagic receiver, pages 42o-422. 

